The present invention relates generally to reinforced structures for use in motor vehicles and, more specifically, relates to lightweight structures for reinforcing hollow structural elements.
In a number of applications in the automotive industry, high-strength structural members with low mass are required. Various composite materials have been proposed in the past as structural members such as exotic light-weight alloys. In most applications, however, mass reduction must not be at the expense of strength and must be balanced against the cost of the product to the consumer. Thus there is a need for maintaining or more preferably for increasing the strength of structural members without significantly increasing materials and labor costs.
The reinforcement of motor vehicle structural members through the use of composite materials is also known. For example the present inventor has disclosed a number of metal/plastic composite structures for use in reinforcing motor vehicles; components. In U.S. Pat. No. 4,901,500 entitled xe2x80x9cLightweight Composite Beamxe2x80x9d a reinforcing beam for a vehicle door is disclosed which comprises an open channel-shaped metal member having a longitudinal cavity which is filled with a thermoset or thermoplastic resin-based material. In U.S. Pat. No. 4,908,930 entitled xe2x80x9cMethod of Making a Torsion Barxe2x80x9d a hollow torsion bar reinforced by a mixture of resin with filler is described. The tube is cut to length and charged with a resin-based material.
In U.S. Pat. No. 4,751,249 entitled xe2x80x9cReinforcement Insert for a Structural Member with Method of Making and Using the Samexe2x80x9d a precast reinforcement insert for structural members is provided which is formed of a plurality of pellets containing a thermoset resin with a blowing agent. The precast member is expanded and cured in place in the structural member. In U.S. Pat. No. 4,978,562, entitled xe2x80x9cComposite Tubular Door Beam Reinforced with a Syntactic Foam Core Localized at the Mid Span of the Tubexe2x80x9d a composite door beam is described which has a resin-based core that occupies not more than one-third of the bore of a metal tube.
In U.S. Pat. No. 4,019,301 entitled xe2x80x9cCorrosion-Resistant Encasement For Structural Membersxe2x80x9d a piling or other structure is disclosed in which an I-beam is encased in a housing into which a resin is poured.
In U.S. Pat. No. 5,575,526 entitled xe2x80x9cComposite Laminate Beam for Automotive Body Construction,xe2x80x9d a hollow laminate beam characterized by high stiffness-to-mass ratio and having an outer portion which is separated from an inner tube by a thin layer of structural foam is described. In U.S. Pat. No. 5,755,486 entitled xe2x80x9cComposite Structural Reinforcement Member,xe2x80x9d a W-shaped carrier insert reinforcement which carries a foam body is described for use in reinforcing a hollow beam.
In addition a number of metal laminates constructions are known in which that metal plates are bonded together by an intervening layer of resin. It is also known to form a metal laminate sheet for use as a floor panel member which comprises a pair of flat metal sheets having an intervening layer of asphalt or elastic polymer.
Although filling the entirety of a section with plastic foam does significantly increase section stiffness (at least when high-density foams are utilized), they also increase mass and thus part weight which, as stated is an undesirable feature in automotive applications. Moreover, although increasing the metal gauge of a section or adding localized metal reinforcements will increase stiffness, as the metal thickness increases, it is more difficult to form the part due to limitations of metal forming machines. Importantly, in many applications increasing metal gauge will not work effectively because mass and stiffness are increased proportionately, with no resultant change in the dynamic stiffness frequency of the part.
Finally, filling a section entirely with foam may be prohibitively expensive, creates a large heat sink and requires elaborate sealing operations to close access holes in the stampings.
Accordingly, it would be desirable to provide a low-cost technique for reinforcing a hollow structural member without proportionately increasing the mass. The present invention provides sections which have increased strength with only moderate increases in mass and without the use of high volumes of expensive resins. In many applications, the present invention reduces vibrations which cause unwanted xe2x80x98shakexe2x80x99 of a component which is primarily subjected to bending rather than torsion.
In one aspect the present invention provides a reinforced structural member for automotive applications. The reinforced structure is a hollow beam such as a rail section or the like having a pair of opposed inner surfaces. The hollow beam is reinforced through the use of a specially formed insert. The insert is a beam (preferably linear) having two opposed plates which substantially span the width of the cavity defined by the walls of the hollow structural member. The opposed plates preferably have generally planar surfaces. A layer of thermally expandable foam with adhesive properties is bonded to each of these planar surfaces. The insert is placed in the cavity of the hollow structural member such that the adhesive layers are adjacent the opposed inner surfaces of the hollow beam. The beam with the reinforcing insert is then heated to thermally activate the expandable adhesive layers. As the adhesive layers expand they bond securely to the inner surfaces of the hollow beam to form an integral structure, i.e. a structurally reinforced beam.
In one aspect the reinforcing insert of the present invention is wholly enclosed in the hollow structural member. In that aspect the insert is dropped into an open channel which is then closed with a top plate.
In one aspect the reinforcing insert of the present invention is an I-beam which is formed of metal, glass filled nylon or a cementitious material that contains microspheres.
Thus, in accordance with the present invention there is provided in one aspect a reinforced structural member, comprising a structural member defining a space, the structural member having two opposed walls; a reinforcing beam disposed in the space, the reinforcing beam having two opposed plates, each of the plates having a principal surface the plates being separated by a predetermined distance with the principal surfaces being approximately parallel to one another and the plates being interconnected by an interconnecting structural spacing element; a first thermally expanded adhesive body disposed on one of the principal surfaces and a second thermally expanded adhesive body disposed on another of the principal surfaces; and the first thermally expanded adhesive body being bonded to one of the walls of the structural member and the second thermally expanded adhesive body being bonded to another of the walls of the structural members.
These and other advantages and objects of the present invention will now be more fully described with reference to the drawings.